Digitizer, stylus and method of synchronization therewith

ABSTRACT

A method for operating a digitizer with an autonomous asynchronous stylus includes sampling outputs from a digitizer, detecting from the outputs at least one pulsed signal transmitted from an autonomous asynchronous stylus at a defined rate, determining a location of the stylus interaction with respect to the digitizer, and tracking stylus interaction with the digitizer over subsequent pulsed signals transmitted from the stylus.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/909,118 filed on Jun. 4, 2013 which is a continuation of U.S. patentapplication Ser. No. 12/643,004 filed on Dec. 21, 2009, now U.S. Pat.No. 8,481,872, which claims the benefit of priority under section 35U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/193,751filed on Dec. 22, 2008. The contents of the above applications areincorporated herein by reference.

FIELD OF THE INVENTION

The present invention, in some embodiments thereof, relates to digitizersensors, signal transmitting styluses used for interaction withdigitizer sensors and more particularly, but not exclusively tosynchronization between signal transmitting styluses and digitizersensors.

BACKGROUND OF THE INVENTION

Electromagnetic styluses are known in the art for use and control of adigitizer. Position detection of the stylus provides input to acomputing device associated with the digitizer and is interpreted asuser commands. Position detection is performed while the stylus tip iseither touching and/or hovering over a detection surface of thedigitizer. Often, the digitizer is integrated with a display screen anda position of the stylus over the screen is correlated with virtualinformation portrayed on the screen.

PCT Patent Publication No. WO2008086058 entitled “Multiple StyliAnnotation System,” the contents of which is incorporated herein byreference, describes an apparatus for stroke capture and retrieval thatworks with an annotation capture and recording system that can operatewith several styli active at the same time. The apparatus includes atleast one ultrasound signal sensor operative to receive ultrasoundsignals from one or more styli when the one or more styli are operatingin a defined working area of the apparatus and at least oneelectromagnetic receiving unit operative to receive electromagneticsignals from an electromagnetic transmitter of the stylus. Coordinationbetween the apparatus and a plurality of styli is provided by acontroller that instructs each of the styli to transmit its ultrasoundsignal at a dedicated time slot. Positioning is determined and trackedbased on received ultrasound signals.

U.S. Pat. No. 7,292,229 entitled “Transparent Digitizer” which isassigned to N-trig Ltd., the contents of which is incorporated herein byreference, describes a passive electro-magnetic stylus which istriggered to oscillate at a resonant frequency by an excitation coilsurrounding a digitizer. The oscillating signal is sensed by thedigitizer. The stylus operates in a number of different states includinghovering, tip touching, right click mouse emulation, and erasing. Thevarious states are identified by altering the resonant frequency of thestylus so that the stylus resonates at a different frequency in eachstate. A position of the stylus, e.g. a position of the stylus' tip withrespect to the digitizer sensor is determined based on signals sensedfrom sensor.

U.S. Patent Application Publication No. 2008/0128180 entitled “PositionDetecting System and Apparatuses and Methods for Use and ControlThereof” assigned to N-Trig Ltd., the contents of which is incorporatedherein by reference, describes an electromagnetic stylus that emitssignals at an oscillation frequency that can be picked up by a digitizersensor and used to determine its position on the sensor. The stylusincludes a variable element, e.g. a resistor, capacitor, or an inductor,that is responsive to pressure exerted on the stylus tip by the user andtriggers changes in the frequency emitted by the stylus. The digitizersystem is operable to discern between different frequencies emitted bythe stylus to determine a position of the stylus and a pressure exertedon the stylus tip by the user.

US Patent Application Publication No. 2008/0238885 entitled “System andmethod for multiple object detection on a digitizer system” assigned toN-Trig LTD, the contents of which is hereby incorporated by reference,describes a digitizer system including at least one object with anelectronic tag configured for radiating at least one modulated signaland at least one second signal; a digitizer sensor configured fordetecting the at least one second signal while the object is positionedon or over the digitizer sensor; and circuitry configured foridentifying the object based on modulation of the at least one modulatedsignal and for determining a position of the object on or over thedigitizer based on the detected second signal on a portion of thedigitizer sensor. Optionally, the modulated signal is transmitted inresponse to an excitation signal.

U.S. Pat. No. 5,571,997 entitled “Pressure sensitive pointing device fortransmitting signals to a tablet” the contents of which is incorporatedherein by reference, describes a pressure sensitive pointing device orpen for use with an electronic tablet that determines the position ofthe pointing device on the surface of the tablet. The pointing deviceincorporates a variable reluctance circuit responsive to the forceexerted on the pen point for modulating a radiating frequency, emanatingfrom the pen, in proportion to the force.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present inventionthere is provided a method for operating a digitizer sensor with anautonomous asynchronous stylus that transmits signal bursts at a definedrate. As used herein, an autonomous asynchronous stylus refers to astylus that generates a transmitting signal that is not triggered byand/or synchronized with a signal transmitted from the digitizer ordigitizer related circuitry. According to some embodiments of thepresent invention, the signal burst is a modulated signal, e.g. itincludes encoded information regarding an operational state of thestylus and/or user command. According to some embodiments of the presentinvention there is provided a digitizer operable to detect signal burststransmitted by a stylus in an operating vicinity of a digitizer and tosample the detected signal bursts.

An aspect of some embodiments of the present invention is the provisionof a method for operating a digitizer with an autonomous asynchronousstylus, the method comprising: sampling outputs from a digitizer;detecting from the outputs at least one pulsed signal transmitted froman autonomous asynchronous stylus at a defined rate; determining alocation of the stylus interaction with respect to the digitizer; andtracking stylus interaction with the digitizer over pulses transmittedpulsed signals transmitted from the stylus.

Optionally, the method comprises determining timing of the detectedpulsed signal within a refresh cycle of the digitizer; and synchronizingthe refresh cycles of the digitizer with the timing of the receivedpulsed signal.

Optionally, the method includes simultaneously detecting finger touchinteraction and the stylus interaction with the digitizer.

Optionally, the finger touch interaction is detected with at least oneof a single touch detection method and a multi-touch detection method.

Optionally, the digitizer switches from detection using a multi-touchdetection method to detection using a single touch detection method inresponse to detection of a stylus pulsed signal.

Optionally, the method includes simultaneously detecting conductiveobject interaction and stylus interaction with the digitizer.

Optionally, the digitizer includes a grid based digitizer sensorincluding conductive lines arrayed along a first and second axis of thedigitizer sensor.

Optionally, timing of the detected pulsed signal is determined fromoutput obtained from 1-4 selected conductive lines from which the pulsedsignal is most strongly detected.

Optionally, the method includes triggering at least a portion of theconductive lines with a triggering signal, and detecting finger touchinteraction in response to the triggering.

Optionally, the method includes synchronizing triggering of theconductive lines with timing of the detected pulsed signal.

Optionally, the method includes sampling conductive lines arrayed alongthe second axis of the digitizer sensor in response to triggering of aconductive line arrayed along the first axis of the digitizer sensor.

Optionally, the timing of a stylus signal is determined based on outputsampled from only one of the first or second axis of the digitizer.

Optionally, the method includes sampling a digitizer over a plurality ofchunk sampling periods, wherein the plurality of chunk sampling periodscover a full transmission cycle of a stylus pulsed signal over aplurality of refresh cycles of the digitizer.

Optionally, the synchronizing is performed while the stylus is hoveringover the digitizer.

Optionally, the method includes adjusting the synchronizing duringtracking of the stylus based on timing of pulsed signals received in thesubsequent refresh cycles.

Optionally, the output is sampled over at least one chunk samplingperiod during each refresh cycle of the digitizer.

Optionally, the method includes substantially synchronizing the chunksampling periods of the digitizer with the timing of the detected pulsedsignal.

Optionally, the method includes initiating the chunk sampling periods ofthe refresh cycles of the digitizer at a predetermined period before thetiming of the detected stylus pulsed signal within the refresh cycle ofthe digitizer.

Optionally, a transmission cycle of the stylus varies for differentoperational modes of the stylus and wherein the digitizer is operativeto detect and track the stylus pulsed signal at varying transmissioncycles.

Optionally, the pulsed signal comprises an AC burst signal of apre-defined frequency.

Optionally, the digitizer detects the pulsed signal of the stylus basedon detection of the pre-defined frequency.

Optionally, the detecting comprises running a DFT window tuned to thepre-defined frequency on the outputs sampled during at least one refreshcycle.

Optionally, the method comprises determining an operational state of thestylus from the detected pulsed signal.

Optionally, the stylus transmits a train of pulsed signals transmittedin succession over a transmission cycle of the stylus and wherein thedigitizer samples the train of pulsed signals over a refresh period ofthe digitizer.

Optionally, at least one of the pulsed signals in the train of pulsedsignal includes encoded information.

Optionally, the encoded information is selected from the groupincluding: identification of the stylus, right click mode of the stylus,eraser mode of the stylus, pressure on tip of the stylus, and userselected color.

Optionally, the method includes decoding information encoded in at leastone stylus pulsed signal from the outputs.

An aspect of some embodiments of the present invention is the provisionof a method for operating a digitizer with an autonomous asynchronousstylus, the method comprising: receiving pulsed signals by the digitizerfrom the autonomous stylus; determining a location on the digitizer fromwhich the pulsed signal is detected; and tracking stylus interactionwith the digitizer over subsequent refresh cycles.

Optionally, the method comprises simultaneously detecting finger touchinteraction and stylus interaction, wherein the stylus interaction isperformed with the asynchronous stylus.

Optionally, the finger touch interaction is detected with at least oneof a single touch detection method and a multi-touch detection method.

An aspect of some embodiments of the present invention is the provisionof a method for operating a digitizer with an autonomous asynchronousstylus, the method comprising: receiving pulsed signals by the digitizerfrom the autonomous stylus, said signals including information;determining a location on the digitizer from which the pulsed signal isdetected; and detecting finger touch interaction with the digitizer.

An aspect of some embodiments of the present invention is the provisionof a digitizer system operated with an asynchronous stylus comprising: adigitizer sensor that receives signals; a stylus that transmitsautonomous asynchronous signals, said signals including information onan operational state of the stylus; and a processor in the digitizersystem that determines position coordinates on the digitizer sensor andthe operational state of the stylus from the received signals.

Optionally, the digitizer sensor senses finger touch interaction andwherein the processor determines position coordinates of the fingertouch interaction.

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a simplified block diagram of an exemplary signal transmittingstylus in accordance with some embodiments of the present invention inaccordance with some embodiments of the present invention;

FIGS. 2A-2C are simplified exemplary time lines showing transmissionpulses transmitted by a stylus in accordance with some embodiments ofthe present invention;

FIG. 3 is a simplified diagram of a digitizer system for use with asignal transmitting stylus in accordance with some embodiments of thepresent invention;

FIG. 4 is a simplified circuit diagram of an exemplary digitizer sensorincluding differential amplifiers for use with some embodiments of thepresent invention;

FIG. 5 is a simplified circuit diagram for exemplary touch detectionbased on a single touch detection method for use with some embodimentsof the present invention;

FIG. 6 is a flow chart describing an exemplary method for detectingpulses received by an autonomous asynchronous signal transmitting stylusin accordance with some embodiments of the present invention;

FIGS. 7A-7B is a simplified time line showing exemplary chunk samplingperiods used during coarse detection in accordance with some embodimentsof the present invention;

FIGS. 8A-8B is a simplified time line showing exemplary chunk samplingperiods used during coarse detection for a stylus that transmits pulsesat a same rate as a refresh rate of a receiving digitizer in accordancewith some embodiments of the present invention;

FIG. 9 is a simplified time line showing exemplary chunk samplingperiods of a digitizer after synchronization with a detected stylus inaccordance with some embodiments of the present invention;

FIG. 10 is a simplified circuit diagram for touch detection based on amulti-touch detection method for use with some embodiments of thepresent invention;

FIGS. 11A and 11B are simplified circuit diagrams for exemplary touchdetection based on a multi-touch detection method with differentialamplifiers for use with some embodiments of the present invention;

FIG. 11C is a time line showing exemplary chunk sampling periods formulti-touch detection method with differential amplifiers for use withsome embodiments of the present invention;

FIG. 12A is a schematic illustration of digitizer sensor outputs along asecond axis of a digitizer sensor in response to simultaneouslytriggering sensor lines along a first axis used to identify interactinglines of the sensor along the second axis in accordance with someembodiments of the present invention;

FIG. 12B is a schematic illustration of sensor outputs when scanninginteracting lines of the second axis of the sensor to determinemulti-touch interaction in accordance with some embodiments of thepresent invention;

FIG. 12C is an exemplary time line of exemplary chunk sampling periodsfor a shortened method for multi-touch detection method withdifferential amplifiers for use with some embodiments of the presentinvention;

FIGS. 13A-13B is a simplified exemplary time line for detecting a styluspulse after repeated refresh cycles of a digitizer scanning 10 selectedlines in accordance with some embodiments of the present invention; and

FIG. 14 is a simplified exemplary time line for supporting multi-touchdetection with detection of an autonomous asynchronous stylus aftersynchronization in accordance with some embodiments of the presentinvention.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to digitizersensors, signal transmitting styli used for interaction with digitizersensors and more particularly, but not exclusively to synchronizationbetween signal transmitting styluses and digitizer sensors.

An aspect of some embodiments of the present invention, provides for adigitizer that can operate with an autonomous asynchronous transmittingstylus. In some exemplary embodiments, the stylus transmits a signalburst that is modulated. Optionally, the signal burst includes a trainof modulated signals, e.g. bursts encoding information regarding one ormore operational states of the stylus and/or user commands. Optionally,a synchronization signal and/or beacon signal is included in the signalburst and is used for synchronizing the digitizer with the stylus.Optionally, the synchronization signal is also used by the digitizer asa positioning signal for locating and tracking the stylus and/or stylusinteraction with respect to the digitizer sensor. Typically the stylusis self-powered, e.g. battery operated.

The present inventors have found that energy consumption of a stylusthat periodically transmits short signal bursts as is described hereinis significantly less than styli that transmits a continuous signalduring their operation as are known in the art. By reducing the energyconsumption, a battery life of the stylus can be increased.

An aspect of some embodiments of the present invention provides forsynchronizing a refresh cycle of a digitizer with a transmission periodof an autonomous stylus. Optionally, the refresh cycle of the digitizeris synchronized with a synchronization signal transmitted by the stylus.According to some embodiments of the present invention, the stylustransmits a signal burst including a synchronization signal during eachtransmission period of the stylus. The length of the transmission periodtypically matches a refresh period of the digitizer and/or is typicallya multiple integer of a length of the refresh period of the digitizer.

According to some embodiments of the present invention, synchronizationof the stylus and digitizer is provided without requiring transmissionof a triggering signal, (and/or excitation pulse) from an excitationcoil (or other transmitter) associated with the digitizer for providingthe triggering signal or optionally other signal to the stylus. Thepresent inventors have found that the cost as well as the dimensions ofthe digitizer can be reduced by eliminating the elements for triggeringthe stylus. Energy consumption of the digitizer system without thetriggering element for triggering the stylus is also significantlyreduced. Typically, triggering occupies a portion of a cycle time of thedigitizer, e.g. 2.5 msec. If triggering is avoided, the cycle timeallotted to transmit the triggering signal, e.g. 2.5 msec can be saved.In addition, the triggering signal emitted typically drives relativelyhigh signals on the sensor lines of the digitizer, which could causesaturation. Typically, to avoid sampling when the output is saturated ablanking period is imposed that typically overlaps with part of atransmission period of the stylus. In some embodiments of the presentinvention, a blanking period of the digitizer sensor typically requiredwhile transmitting a triggering signal can also be avoided.

According to some embodiments of the present invention, a presence of astylus within an operating range of the digitizer is identified during asearch mode (coarse detection mode) of the digitizer. In some exemplaryembodiments, during a search mode a digitizer alternates chunk samplingperiods over which input to the digitizer is sampled so that an entireduration of a stylus transmission period is sampled over a plurality ofrefresh cycles of the digitizer. As used herein, a chunk sampling periodis a duration over which output from the digitizer sensor is sampled.Typically, the digitizer output is repeatedly sampled at a definedsampling rate, e.g. 100 KHz or 200 KHz during each chunk samplingperiod. Optionally, the chunk sampling periods partially overlap.Typically, timing of a received stylus pulse is approximated, e.g.determined coarsely during this search mode. Optionally, other userinteractions, e.g. finger touch interaction and/or conductive objectinteraction, concurrently interacting with the digitizer sensor aretracked during a search mode period of the digitizer. Typically, methodsapplied to detect conductive object interaction are similar and/or thesame as the methods applied to detect finger touch interaction. In someexemplary embodiments, when a stylus is identified during a search mode,tracking positioning of stylus is initiated based on the received styluspulse. Tracking is provided although the timing of the stylus pulse,e.g. the onset of the received pulse, may not be preciously determined.

In some exemplary embodiments, in response to receiving signals from astylus within one or more of the chunk sampling periods, a finer tunedsearch is performed over subsequent refresh cycles using a filteringwindow stepped around the time vicinity of the identified signal todetermine an onset of reception. Optionally, fine tuning is performed onoutput obtained close to an identified location of the stylus. Accordingto some embodiments of the present invention, a refresh period of thedigitizer is synchronized, e.g. adjusted to coincide with, the detectedonset of signal reception from the stylus.

Typically, once synchronization is established, the digitizer operatesin a tracking mode where it tracks the detected stylus as well as anyother user interactions concurrently interacting with the digitizer,e.g. finger tip. Typically, during track mode a single chunk samplingperiod for sampling.

Optionally, input received from the stylus is processed to determineinformation encoded by signal modulation. Encoded information mayinclude for example, identification data, pressure state of the stylustip, right click mode, erase mode, selected color, hover and/or touchtype interaction. Optionally, during a tracking mode synchronizationbetween the digitizer and identified stylus is periodically adjusted asrequired.

Reference is now made to FIG. 1 showing a simplified block diagram of anexemplary signal transmitting stylus in accordance with some embodimentsof the present invention. According to some embodiments of the presentinvention, a stylus 44 is an autonomous asynchronous device thattransmits pulses of energy, e.g. an electric signal generated with apulse generator 420 with a transmitting unit 460. According to someembodiments of the present invention, pulse generator 420 generates oneor more AC signal bursts providing pulsed signals (AC pulses), e.g. atrain of pulses (signal bursts). Optionally, the AC pulses have afrequency content selected between 20-40 KHz. Typically, pulse generator420 generates pulses having a frequency content other than thefrequencies typically used to detect finger touch on a digitizer.Typically, a frequency of burst signal of stylus 44 is orthogonal to thefrequencies typically used to detect finger touch in the sampling spaceor far enough away so that simultaneous user interaction (finger andstylus) may be possible. Optionally, specific time slots for fingertouch detection and stylus are defined to avoid close frequencies. Insome exemplary embodiments, pulse generator 420 generates pulses havinga width between 1-2 msec, e.g. 1.28 msec.

According to some embodiments of the present invention, stylus 44 ispowered by power source 405. Typically, power source 405 includes one ormore batteries, e.g. 4A alkaline battery. Optionally rechargeablebatteries are used. Optionally, a voltage stabilizer also included instylus 44 is used to stabilize voltage from power source 405.

According to some embodiments of the present invention, stylus 44includes a power switch 401 for powering transmission of stylus 44 andone or more operational switches and/or dials 402 for receivingoperation commands from a user. Typically switches 402 control rightclick and eraser mode commands as well as color selection when writingor drawing with the stylus. Optionally, a rocker switch is used forright click or eraser operation, e.g. at least one of switches 402 is arocker switch.

Optionally, tip 440 of stylus 44 is operative as an antenna oftransmission unit 460 and/or an electric dipole. For example, one outputof pulse generator 420 is electrically connected to stylus tip 440(typically constructed from a conductive material) while the other endis electrically connected to a frame 4411 (which likewise comprisesconductive material) surrounding tip 440. Typically, frame 4411 isintegral to housing 441 and is grounded. An electric field, synchronizedto a generated signal pulse, is formed in a small gap 442 locatedbetween the tip 440 and the frame 441. The geometric dimensions of thegap and the consequent field are relatively small so that the fieldsource can be substantially close to the stylus tip and thereby providea concentrated signal at the tip. Signals transmitted by the stylus canbe picked up at a relatively concentrated point by a digitizer or othersensing surface and the position of the stylus at that position can beconveyed to the digitizer. Optionally, stylus 44 includes a separateantenna and does not use tip 440 for transmitting output signals.

Optionally, stylus 44 is a pressure sensitive stylus that transmitsinformation regarding contact pressure applied to tip 440. In someexemplary embodiments, tip 440 recedes into housing 441 in axialdirection 50 in response to applied contact pressure by a user operatingthe stylus, e.g. pressing tip on a surface and is subsequently releasedwhen the contact pressure is released, e.g. a hovering state ornon-operational state of the stylus. Typically, during axial movementtip 440 is engaged with a resilient element 443, e.g. a spring whoseproperties are selected to obtain a desired relationship between contactpressure and axial displacement.

In some exemplary embodiments, a pressure sensor unit 410 senses contactpressure applied to tip 440 and based on sensed contact pressure level,a frequency content of a pulse generated by pulse generator 420 isaltered and/or defined. In some exemplary embodiments, a specificfrequency band is allocated for transmitting pressure information. Forexample within the frequency band of 20-40 KHz, e.g. 20-25is allocatedfor transmitting pressure information. Optionally, output from pressuresensor unit 410 is encoded with encoder 430 on pulse generated by pulsegenerator 420.

According to some embodiments of the present invention, encoder 430 is adigital encoder operable to encode an operational state of stylus 44and/or identification information of stylus 44 into a pulse generated bypulse generator 420. Typically, operational state of stylus 44 isobtained from switch state of switches 402. Optionally, pressure stateof the digitizer is encoded with encoder 430. One or more encodingmethods selected from Amplitude Shift Keying (ASK), Phase Shift Keying(PSK) and Frequency Shift Keying (FSK) may be used to encode informationwith encoded 430. In some exemplary embodiments, encoded information istransmitted over a plurality of transmission cycles. For example one bitof encoded information is transmitted per transmission cycle.

According to some embodiments of the present invention, pulse generator420, encoder 430 and pressure sensor unit 440 and/or their functionalityare embedded in an ASIC unit 450.

According to some embodiments of the present invention, a time betweenpulses matches a refresh cycle of a digitizer or an integer multiple ofa refresh cycle of a digitizer, e.g. twice a refresh cycle of adigitizer and/or three of four times a refresh frequency of a digitizer.Optionally, a time between pulses (bursts) is variable and iscontrollably altered based on an operational state of the digitizer.

Reference is now made to FIGS. 2A, 2B and 2C showing simplifiedexemplary time lines showing transmission pulses transmitted by a stylusin accordance with some embodiments of the present invention. Referringfirst to FIG. 2A, in some exemplary embodiments, stylus 44 transmits apulse 110 once over a stylus transmission period T_(S). According tosome embodiments of the present invention, pulse 110 is an AC signalburst of a predefined width, e.g. duration. Optionally, T_(S) is definedto be twice a refresh cycle or period of a receiving digitizer T_(D) sothat a digitizer receiving signals from stylus 44 will potentiallyreceive a signal every other refresh cycle T_(D) of the digitizer. Insome exemplary embodiments, stylus 44 transmits signals every 15 msec(T_(S)=15 msec) to a digitizer that samples its signals every 7.5 msec(T_(D)=7.5 msec). In some exemplary embodiments, pulse 110 is a beaconpulse used to locate a position of tip 440 in relation to a digitizerreceiving pulse 110 and/or to synchronize the digitizer with timing ofthe stylus pulses (AC burst signals). Typically, pulse 110 istransmitted at a pre-defined amplitude, e.g. 20 V and frequency and doesnot include encoded information. Typically, the digitizer can identify astylus pulse with amplitude in the order of about 1 mV. In someexemplary embodiments, a transmission pattern as shown in FIG. 2A isused while stylus 44 is hovering over a digitizer and none of rightclick mode or eraser mode is selected (with operational and/or selectionswitches 402). In some exemplary embodiments, a lower rate for repeatingtransmission of stylus' pulses and/or lower accuracy of the stylusposition during hover mode is used in exchange for reduced energyconsumption of the stylus as well as the detecting digitizer.Optionally, a frequency of transmission of pulse 110 is altered based onoperational state of stylus 44 and/or its battery life.

Referring now to FIG. 2B, in some exemplary embodiments, stylus 44transmits an additional pulse 120 (or pulses) that trails a first pulse110. Typically, a signal burst represented by trailing pulse 120 differsand/or is distinguished from beacon pulse 110 by frequency of its ACburst signal and/or phase of its AC burst signal. In some exemplaryembodiments, trailing pulse 120 is an analogue encoded burst signal. Insome exemplary embodiments, trailing pulse 120 provides informationregarding an operational state of stylus 44. Optionally, trailing pulse120 indicates a right click or eraser operational state of stylus 44. Insome exemplary embodiments, AC signal burst 110 and 120 have a samefrequency of oscillation and information embedded in pulse 120 (digitalor analog encoding) is derived from a phase of the AC burst signal ofpulse 120 in relation to a phase of the AC burst signal of pulse 110.Optionally, 0 degree phase shift indicates right click mode command anda 180 degree phase shift indicates eraser mode command. According tosome embodiments of the present invention, a scalar product of an energyvector measured for pulse 110 by the digitizer and an energy vectormeasured for pulse 120 by the digitizer is determined. If there is aninteger number of cycles included in the pulses and the scalar productis positive than most likely pulse 120 is in phase with pulse 110, e.g.0 degree phase shift, otherwise pulse 120 is most likely shifted by a180 degree phase shift. Optionally, the phase can be determined bymajority voting. According to some embodiments of the present invention,determining an operational state of the stylus, e.g. right click oreraser mode, based on differences in phase between AC signal burst 110and 120 avoids errors associated with locking on the exact timing of theonset of AC signal burst 110 and the onset of AC signal burst 120 thatdirectly trails AC signal burst 110. By using the same frequency as thebeacon signal for right click and erase commands, more frequencies areavailable for encoding additional information, e.g. pressure tipinformation. Typically, the frequency band of the stylus is limitedsince frequencies used for finger detection are avoided. Alternatively,a frequency of the AC signal of pulse 120 is indicative of theinformation supplied by pulse 120.

Referring now to FIG. 2C in some exemplary embodiments, a timing betweentransmission of stylus pulses is increased, e.g. doubled, while thestylus 44 is in tip mode, e.g. contact pressure is detected on stylustip 440 and none of right click mode or eraser mode is selected, e.g.with switches 402. Optionally, during a tip mode, stylus 44 alternatesbetween transmitting a beacon signal 110 and a pressure pulse 150indicating a pressure level on tip 440. In some exemplary embodiments,pressure is an AC signal with a frequency related to a pressure leveldetected by stylus 44. According to some embodiments of the presentinvention, pressure pulse 150 includes frequencies that are orthogonalor far away enough away from frequencies used for touch detection toenable simultaneous detection of stylus pressure and touch. Optionally,dedicated time slots, e.g. time division is used for sampling of styluspressure and touch so that they can be differentiated.

Optionally, pressure pulse 150 is a digitally encoded pulse indicatingone out of a plurality of defined pressure levels.

According to some embodiments of the present invention, during a tipmode a trailing pulse 130 following a beacon pulse 110 transmitsadditional information to a receiving digitizer, e.g. identification,and color for tracing. Optionally, trailing signal 130 encodes one bitof digitally encoded signal for providing additional information to areceiving digitizer. Optionally, while the pen is in right click modeand/or eraser mode, pressure pulse 150 and digitally encoded pulse 130are not transmitted.

According to some embodiments of the present invention, each of pulses,110, 120, 130, 150 have a same width. Optionally, a 1.28 msec pulsewidth is used for each transmission pulse. Typically, detection isestablished in a hover mode where the signal to noise ratio is typicallyless than that of a tip mode. In some exemplary embodiments, a stylus isidentified while its tip is hovering over the digitizer at a height ofup to 15-20 mm. Optionally, amplitude of pressure pulse 150 is the sameas beacon signal 110. Optionally, amplitude of pulses transmitted by thestylus is reduced during a tip operation mode, e.g. above a pre-definedtip pressure to reduce energy expenditure. Since the signal noise ratioduring a tip operational mode is greater than the signal to noise duringa hover state a lower amplitude may be sufficient for detection.

According to some embodiments of the present invention, patterns oftransmission pulses from a stylus and information transmitted from astylus may be similar to those described in U.S. patent application Ser.No. 12/546,753 entitled “Pressure sensitive stylus for a digitizer,”assigned to N-Trig, and the contents of which is incorporated herein byreference.

Reference is now made to FIG. 3 showing a simplified block diagram of adigitizer system for use with a signal transmitting stylus in accordancewith some embodiments of the present invention. The digitizer system 100shown in FIG. 3 may be suitable for any computing device that enablesinteractions between a user and the device, e.g. mobile computingdevices that include, for example, FPD screens. Examples of such devicesinclude Tablet PCs, pen enabled lap-top computers, PDAs or any hand helddevices such as palm pilots and mobile phones. According to someembodiments of the present invention, the digitizer system is operativeto detect multiple inputs from one or more styli 44, finger(s) 46 and/ora conductive object(s) 45. According to some embodiments of the presentinvention, stylus 44 is an autonomous asynchronous stylus thatperiodically transmits signal bursts and/or pulses.

According to some embodiments of the present invention, the digitizersystem comprises a sensor 12 including a patterned arrangement ofconductive lines (sensor lines), which is optionally transparent, andwhich is typically overlaid on a FPD 10. Typically sensor 12 is a gridbased sensor including horizontal and vertical conductive lines.Optionally, a width of the conductive lines varies over its length. Insome exemplary embodiments, a width of the conductive lines are narroweraround the vicinity of junction points of the grid and wider betweenjunction points. Optionally, the conductive lines are shaped likediamond shape array with diamond points are matched to junction points.

Typically, the parallel conductive lines are equally spaced straightlines, and are input to amplifiers included in ASIC 16. Optionally theamplifiers are differential amplifiers. Typically, the parallelconductive lines are spaced at a distance of approximately 2-8 mm, e.g.4 mm, optionally depending on the size of the FPD and a desiredresolution.

An ASIC 16 comprises circuitry to process and sample the sensor's outputinto a digital representation. The digital output signal is forwarded toa digital unit 20, e.g. digital ASIC unit, for further digitalprocessing. According to some embodiments of the present invention,digital unit 20 together with ASIC 16 serves as the controller of thedigitizer system and/or has functionality of a controller and/orprocessor. Optionally, a single unit is used—for example in small screenwith limited number of lines. According to some embodiments of thepresent invention, ASICs 16 operate as a detection unit for processingand sampling the sensor's output. The outcome, once determined, isforwarded to a host 22 via an interface 24 for processing by theoperating system or any current application. According to someembodiments of the present invention, control functionality isadditionally or exclusively included in the host 22. ASIC 16 and digitalunit 20 may be provided as a single ASIC. Optionally digital unit 20 andASICs 16 are mounted on a PCB 30, e.g. L-shaped PCB positioned along twosides of sensor 12.

Typically, ASIC 16 is connected to outputs of the various conductivelines in the grid and functions to process the received signals at afirst processing stage. Optionally, instead of PCB 30 positioned alongtwo sides of sensor 12, a flex cable is used to connect the conductivelines to ASICs 16, e.g. positioned away from a sensing surface ofdigitizer 100. As indicated above, ASIC 16 typically includes one ormore arrays of amplifiers, e.g. an array of differential amplifiers, anarray of single ended amplifiers, or an array of differential amplifieroptionally including one grounded input to amplify the sensor's signals.In some exemplary embodiments, the grounding input is selected by ASIC16. Additionally, ASIC 16 optionally includes one or more filters toremove irrelevant frequencies. Optionally, filtering is performed priorto sampling. The signal is then sampled by an A/D, optionally filteredby a digital filter and forwarded to digital ASIC unit, for furtherdigital processing. Alternatively, the optional filtering is fullydigital or fully analog.

According to some embodiments of the invention, digital unit 20 receivesthe sampled data from ASIC 16, reads the sampled data, processes it anddetermines and/or tracks the position of physical objects, such asstylus, and/or finger, touching the digitizer sensor. According to someembodiments of the invention, digital unit 20 is operative to decodeinformation encoded in a signal transmitted by stylus 44, e.g. pressureon tip, right-click and eraser mode, color for tracing, andidentification. According to some embodiments of the present inventionhovering of an object, e.g. stylus, finger and hand, is also detectedand processed by digital unit 20. Calculated position is sent to thehost computer via interface 24.

According to some embodiments of the present invention, digital unit 20is operative to synchronize a refresh cycle of digitizer system 100 witha transmission period of autonomously transmitting stylus 44. Accordingto some embodiments of the present invention, digital unit is operableto switch between different patterns of chunk sampling periods dependingon a detection state of the digitizer for detecting an autonomousstylus, e.g. coarse detection, fine detection and tracking modedetection. Details describing detection of an autonomous stylus andsynchronization of the digitizer is provided herein below.

In some exemplary embodiment, the digitizer system 100 has severalchannels, i.e. interfaces included within interface 24, with the hostcomputer. In an exemplary embodiment, a stylus interface is provided fortransmitting stylus coordinates on the display screen and finger touchinterface is provided for transmitting finger touch coordinates on thedisplay screen. In some exemplary embodiments, finger touch coordinatesbased on both single touch detection method and multi-touch detectionmethod is transmitted on a same interface. Optionally, the interfacetransmits information on detected gestures.

According to some embodiments of the present invention, digital unit 20is operative to control operation of one or more ASIC(s) 16. Accordingto some embodiments of the present invention, digital unit 20 isoperative to provide a command signal to ASIC 16 to switch between aplurality of available circuit paths (two or more) to connect to outputsof the various conductive lines in the grid. In some exemplaryembodiments, digital unit 20 together with ASIC 16 provides foralternately connecting outputs of the various conductors to one of anarray of differential amplifiers and an array of single ended amplifiers(or differential amplifiers with one grounded input). According to someembodiments of the present invention, digital unit 20 is operative tocontrol triggering of one or more conductive lines. According to someembodiments of the present invention, ASIC 16 together with digital unit20 provides for triggering various conductors with an oscillating signalhaving a selected pre-defined frequency or frequencies.

According to some embodiments of the invention, digital unit 20 includesat least a memory unit and a processing unit to store and processinformation obtained from ASIC 16. Memory and processing capability isalso generally included in host 22 and ASIC 16. According to someembodiments of the present invention memory and processing functionalitymay be divided between any two or three of host 22, digital unit 20, andASIC 16 or may reside in only digital unit 20 and host 22.

Stylus Detection

Reference is now made to FIG. 4 showing an array of conductive lines ofthe digitizer sensor as input to differential amplifiers according tosome embodiments of the present invention. According to some embodimentsof the present invention, two parallel sensor lines, e.g. lines 310 and320 that are close but not adjacent to one another are connectedrespectively to the positive input 311 and negative input 321 of adifferential amplifier 340. Amplifier 340 is thus able to generate anoutput signal which is an amplification of the difference between thetwo sensor line signals. An amplifier having a stylus on one of its twosensor lines will produce a relatively high amplitude output. Typicallyoutput is detected on sensor lines in both the X and Y direction tolocate the coordinates of a stylus interacting with sensor 12. In someexemplary embodiments, a single input amplifier is implemented anddifference signal is determined by software embedded in digital unit 20.It is noted that although determining the difference signal by softwaremay provide more versatility it may also limit the dynamic range of thesignal that can be sampled. Optionally the stylus detection is done insingle ended mode.

In some exemplary embodiments, output on sensor lines in both the X andY direction are sampled every 6-9 msec, e.g. 7.5 msec defining a refreshcycle of the digitizer. In some exemplary embodiments, during eachrefresh cycle, sensor lines are sampled at a sampling frequency of 100KHz during a defined chunk sampling period, e.g. 2-4 msec and/or 3.84msec. Optionally, a 200 KHz sampling period is used. Stylus detection isdescribed with further details, for example in incorporated U.S. Pat.No. 7,292,229. It is noted that the differential setup described inreference to FIG. 4 can be applied for stylus detection only,simultaneous finger touch detection and stylus detection. Optionally,the differential setup described in reference to FIG. 4 can be adaptedto multi-touch detection as well.

Finger Touch Detection—Single Touch Detection Method

Reference is now made to FIG. 5 showing an exemplary simplified circuitdiagram for touch detection based on a single touch detection method foruse with some embodiments of the present invention. Conductive lines 310and 320 are parallel non-adjacent lines of sensor 12. According to someembodiments of the present invention, conductive lines 310 and 320 areinterrogated to determine if there is a finger input signal derived fromfinger touch and/or finger hovering. To query the pair of conductivelines, a signal source I_(a), e.g. an AC signal source induces anoscillating signal in the pair. Signals are referenced to a commonground 350. When a finger is placed on one of the conductive lines ofthe pair, a capacitance, C_(T), develops between the finger (eithertouching or hovering over the digitizer) and conductive line 310. Asthere is a potential between the conductive line 310 and the user'sfinger, current passes from the conductive line 310 through the fingerto ground. Consequently a potential difference is created betweenconductive line 310 and its pair 320, both of which serve as input todifferential amplifier 340.

Separation between the two conductive lines 310 and 320 is typicallygreater than the width of the finger so that the necessary potentialdifference can be formed, e.g. approximately 12 mm. Typically a fingertouch on the sensor may span 2-8 lines, e.g. 6 conductive lines.Typically, the finger hovers over and/or touches the digitizer over anumber of conductive lines so as to generate an output signal in morethan one differential amplifier, e.g. a plurality of differentialamplifiers. However, a finger touch may be detected when placed over oneconductive line. Typically a finger hovering at a height of about 1 cm-2cm above the digitizer can be detected. The differential amplifier 340amplifies the potential difference developed between conductive lines310 and 320. ASIC 16 and digital unit 20 process the amplified signaland determine the location and/or position of the user's finger based onthe amplitude and/or signal level of the sensed signal. Although onlyone pair of conductive lines are shown, it is noted that touch istypically detected based on a plurality of outputs from differentialamplifiers with input obtained from interleaving conductive lines.

In one example, the origin of the user's finger from the two inputs ofthe differential amplifier is determined by examining the phase of theoutput. In another example, since a finger touch typically producesoutput in more than one conductive line, the origin of the user's fingerfrom the two inputs of the differential amplifier is determined byexamining outputs of neighboring amplifiers and optionally interpolationis used to find a more accurate value. In yet other examples, acombination of both methods may be implemented. According to someembodiments of the present invention, stylus interaction can be detectedconcurrently with finger touch using this detection method. Typically,the stylus transmits at a frequency other than the frequency used forfinger detection so that finger and stylus detection can bedifferentiated. Typically, all sensor lines are interrogatedsimultaneously and based on sampled outputs on both an X and Y axis ofthe digitizer, coordinates of detected user interaction (finger and/orstylus) are determined. Typically, a refresh cycle of finger detectionis the same as that used for stylus detection during tip mode of thestylus.

According to some embodiments of the present invention, this method oftouch detection which is described with further details in, for exampleincorporated U.S. Pat. No. 7,372,455 is implemented for single touchdetection.

Autonomous Asynchronous Stylus Detection

Reference is now made to FIG. 6 showing a flow chart describing anexemplary method for detecting pulses received by an autonomousasynchronous signal transmitting stylus in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, at start-up or prior to detection of atransmitting stylus, a coarse detection mode for searching for atransmitting stylus is defined and applied by digital unit 20 ofdigitizer system 100 (block 610). According to some embodiments of thepresent invention, during course detection mode, periods for sampling,e.g. chunk sampling periods, are staggered over different portions of arefresh cycle to cover an entire transmission period of a stylus over afew refresh cycles. Typically, characteristics of the expectedtransmission pulse, e.g. frequency of AC signal burst, duration, a timebetween pulses is known and stored by the digitizer, e.g.pre-determined. In some exemplary embodiments, a duration of each chunksampling period is at least 3 times a duration of an expectedtransmission pulse of stylus 44, e.g. 3 times 1.28 msec (3.84 msec).Optionally, a time between pulses is known to alter based on anoperation mode of the stylus, e.g. between once every refresh cycle ofthe digitizer or once every other refresh cycle of the digitizer.

According to some embodiments of the present invention, coarse detectionfor stylus 44 continues while a transmission pulse of stylus 44 is notdetected (block 620). In some exemplary embodiments, during coarsedetection DFT windows (in stylus AC burst signal frequency) are run inrelative large steps, e.g. ¼ a width of an expected transmission pulse,to identify a stylus signal within one of the chunk sampling periods.Typically, during coarse detection, DFT windows are run on outputsobtained from all amplifiers 340 as the stylus position is unknown.

Once a stylus is detected in one of the chunk sampling periods,digitizer 100 enters a fine detection mode (630) to determine start ofthe received transmission with finer accuracy and synchronize the chunksampling periods with determined timings of the stylus' beacon pulse110. Typically, since fine tuning may require heavy processing, finedetection is performed from output sampled on one or a few, e.g. 1-4,selected sensor line on which the stylus was detected and not on all thesensor lines. In some exemplary embodiments, DFT windows (in stylus ACburst signal frequency) that are stepped with relatively small steps areused, e.g. 1/32 a width of an expected transmission pulse to detect anonset of the received stylus signal. In some exemplary embodiments,during fine detection, timing of a received pulse can be identified withan accuracy of about 0.02 msec and/or about 1/64 a width of an expectedtransmission pulse.

According to some embodiments of the present invention, timing of chunksampling periods of the digitizer are synchronized with identifiedtiming of received stylus pulses (block 640) and the digitizer operatesin track mode (block 650). Synchronization is locked once fine detectionis completed (block 640) and is updated and/or adjusted as requiredand/or periodically when fine detection is repeated. Typically duringtrack mode (and find detection mode), the digitizer is sampled duringone chunk sampling period of between 2-4 msec during each refresh cycle,e.g. at the start of each refresh cycle.

Typically, track mode (position reporting of the stylus) is activatedonce a stylus is detected (block 620) and fine detection (block 630) andsynchronization (block 640) is performed in parallel with track mode(block 650). In some exemplary embodiments, finger touch detection isdesired and/ore required, conductive lines of sensor 12 are triggered atthe start of each chunk sampling period and triggering continuesthroughout the chunk sampling period.

Over the course of tracking, if the stylus signal is lost, e.g. notpresent over a pre-defined period of time (block 660), synchronizationis lost and the digitizer reverts back to coarse mode detection (block610).

According to some embodiments of the present invention, during trackmode, synchronization is updated periodically with fine tune detection(block 670). Typically, updating is required to compensate forcumulative errors due to limited accuracy in determining timing ofreceived stylus pulse as well as due to drift between stylus anddigitizer clocks.

It is noted that, finger detection, e.g. based on a single touchdetection mode may be supported during stylus search and tracking and istypically unaffected during coarse and fine detection mode and proceedsat a steady refresh rate. Typically, while the digitizer is synchronizedwith stylus transmission period, timing for finger detection is alsosynchronized with stylus detection. In some exemplary embodiments,conductive lines of sensor 12 are triggered at the start of each chunksampling period once synchronization is established and triggeringcontinues throughout the chunk sampling period.

Reference is now made to FIGS. 7A and 7B showing a simplified exemplarytime line of exemplary chunk sampling periods used during coarsedetection in accordance with some embodiments of the present invention.In some exemplary embodiments, three chunk sampling periods 710, 720 and730 are staggered over three or more transmission periods T_(S) of atransmitting stylus in the following repeatable pattern {710, 720, 730,710, 710, 720, 730}. Typically, all chunk sampling periods have a commonduration that is at least three times a width of an expectedtransmitting pulse of a stylus. Typically, each of chuck samplingperiods 710, 720, and 730 are differentiated by their positioning withina refresh period of the digitizer T_(D). For example chunk samplingperiod 710 is initiated at a pre-defined time after an onset of T_(D),chunk sampling period 720 is initiated at the onset of T_(D), and chunksampling period 730 is initiated toward the end of T_(D) and extendsover to the next T_(D). According to some embodiments of the presentinvention, finger touch position (790) is reported to the host computerduring each digitizer refresh cycle and coinciding with a chunk samplingperiod so that finger tip detection is maintained at a constant refreshrate. Typically, triggering of the sensor lines for finger tip detectionis applied over an entire duration of each chunk sampling period toavoid errors in stylus energy measurement due to partial of thetriggering signal.

According to some embodiments of the present invention, for a systemwhere the stylus transmits once every other refresh cycle of thedigitizer, one full transmission period of the stylus T_(S) (timebetween pulses) is fully covered over a period equally three T_(S).During this period (3 time T_(S)), at least one of the chunk samplingperiods will catch a full width of a transmission pulse of a stylustransmitted once over T_(S). According to some embodiments of thepresent invention, it is desirable to detect a full transmission pulsein at least one chunk sampling period to improve the signal to noiseratio as opposed to parts of the transmission burst signal overdifferent chunk sampling periods.

According to some embodiments of the present invention, the staggeredpattern shown in FIG. 7A provides for overlapping of the chunk samplingperiods over a width of the pulse transmitted by the stylus, e.g. 1.28msec. In FIG. 7B chunk sampling periods over the three stylustransmission cycles (T_(S1), T_(S2), T_(S3)) are shown one over theother so that overlapping between the chunk sampling periods can moreclearly be seen. Chunk sampling period 730 is divided over the upper twotime lines in FIG. 7B since it extends over stylus transmission cycleT_(S1) and T_(S2).

A width between each of the dotted lines (t₁, t₂, . . . t₁₃) constitutea width of an expected transmission pulse received from a stylus, e.g.1.28 msec for a digitizer refresh rate of 7.5 msec. For example if astylus pulse appears between t₂ and t₄, a full width of the stylus pulsecan be detected during T_(S3) in chunk sampling period 720. In anotherexample, if a stylus appears between t₁₀ and t₁₂, a full width of thestylus pulse can be detected during T_(S2) in chunk sampling period 710.

According to some embodiments of the present invention, a same orsimilar repeatable pattern (710, 720, 730, 710, 710, 720, 730) can beused to detect a stylus signal occurring at a lower rate than once everyother refresh cycle of the digitizer. Typically, more than threetransmission periods of the stylus will be required for stylus pulsedetection in such a case.

Reference is now made to FIGS. 8A and 8B showing a simplified exemplarytime line of exemplary chunk sampling periods used during coarsedetection for a stylus that transmits pulses at a same rate as a refreshrate of a receiving digitizer in accordance with some embodiments of thepresent invention. According to some embodiments of the presentinvention, when the stylus transmits at a same frequency as the refreshfrequency of a digitizer a simpler coarse detection pattern is used todetect an appearance of a stylus signal. According to some embodimentsof the present invention, a stylus is detected by similar principles asdescribed in reference to FIGS. 7A and 7B but over 1-2 transmissionperiods of the stylus. According to some embodiments of the presentinvention, a pattern of detection used includes chunk sampling periods(720, 730 and 710) staggered over two transmission periods of thestylus. Overlapping, of at least a width of the stylus pulse issimilarly provided as described in reference to FIGS. 7A and 7B. Forexample when a stylus pulse appears between t3 and t5 it can be fullydetected during T_(S2) in chunk sampling period 730. In another example,when a stylus pulse appears between t1 and t3 it can be fully detectedduring T_(S1) in chunk sampling period 710.

According to some embodiments of the present invention, a filter, e.g. aDFT filter tuned to an AC frequency of the beacon pulse (signal burst)and that has a same and or substantially the same width as a beaconpulse of a stylus is run in each chunk to identify a chunk including afull beacon pulse of the stylus. Optionally, the filter is applied insteps of ¼ of the width of the beacon signal. Steps of ¼ of the width ofthe beacon signal provide for at least detecting 87.5% of thetransmitted signal.

According to some embodiments of the present invention, during finetuning is performed during a subsequent refresh cycle(s) of thedigitizer after a stylus has been detected in coarse search mode.Typically, all sensor lines are sampled to supply position informationon any finger interacting with the digitizer as well as the detectedstylus. According to some embodiments of the present invention, a filteris passed in steps of 1/32 of the width of beacon pulse 110, e.g. 4samples at 100 KHz sampling frequency, on the sampled data starting froma time point in the chunk sampling period just prior to where the styluswas detected, e.g. in the coarse mode detection. In some exemplaryembodiments, filtering is initiated 0.32 msec before the point ofdetection in the previous refresh cycle where the stylus was detected.Since the strongest window in coarse detection may only capture 87.5% ofthe signal, e.g. 112 samples at a 100 KHz sampling rate, filtering forfine tuning should begin 16 samples prior to the strongest window found.However, to provide noise immunity filtering may begin at 32 samplesprior to detection of the strongest window. Typically, fine tuning isperformed on selected lines where the stylus was detected, e.g. thesensor line outputting the strongest stylus signal and based on outputsreceived from those lines, timing of the stylus pulse is determined andused for synchronization.

Reference is now made to FIG. 9 showing a simplified exemplary time lineof an exemplary chunk sampling periods of a digitizer aftersynchronization with a detected stylus in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, a chunk sampling period 700 of a digitizer isdefined to begin a pre-defined period before a stylus beacon pulse 110and/or pressure pulse 150 is expected based on a previous time detectionof stylus beacon pulse. In some exemplary embodiments, if stylus pulse110 is expected at time 990, a chunk sampling period is initiated justbefore it is expected, e.g. 0.32 msec and is extended after the expectedstylus pulse ends. In some exemplary embodiments, initiating chunksampling period 700 before stylus pulse 110 is expected allows for finetuning of start of reception based on received input. It is noted thatfinger reporting 790 doesn't necessarily synchronized with a beginningof a refresh cycle (T_(D)) as shown in FIGS. 7A, 7B, 8A, 8B and 9.

Multi-Touch Detection Method

Reference is now made to FIG. 10 showing an exemplary simplified circuitdiagrams for touch detection based on a multi-touch detection method foruse with some embodiments of the present invention.

According to some embodiments of the present invention, detection of afinger in multi-touch detection is a capacitive-based detection method.At each junction, e.g. junction 40 in sensor 12 a certain minimal amountof capacitance exists between orthogonal conductive lines. When a finger46 touches (or hovers over) the sensor, the capacitance formed injunctions 42 within the vicinity of finger 46 typically increases sincethe finger typically drains current from the lines to ground.

According to some embodiments of the present invention, the change incapacitance at one or more junctions 42 is detected by triggering one ormore parallel conductive lines, e.g. active line(s) 302 of sensor 12with an AC signal 60 and detecting signals 65 crossing by virtue of thecapacitance to crossing lines, e.g. passive lines 301 orthogonal totriggered line 302. Typically, the presence of a finger decreases theamplitude of the coupled signal by 5-15% or 15-30% and thereby can bedetected.

According to some embodiments of the present invention, the procedurefor detection includes triggering each conductive line along one axis ofthe sensor, e.g. each active line 302, one line at a time, and whiletriggering, signals are sampled, e.g. simultaneously in all linescrossing that triggered line, e.g. all lines of the orthogonal axis(passive lines 301). This triggering and detecting procedure is repeateduntil all the lines in the active axis have been triggered andinteraction in all junction points has been detected.

This multi-touch detection method constructs two dimensional images thatindicate positions of a plurality of fingers (and conductive objects)concurrently interacting with sensor 12. Typically, such an imageindicates on which junction an interaction, e.g. a touch is present.

Optionally, multi-touch detection is provided in specified pre-definedareas of sensor 12 and only the active line and passive lines crossingthe pre-defined areas are triggered and sampled. In some exemplaryembodiments, multi-touch detection provides for simultaneously triggermore than one line with different frequencies and/or phase as isdescribed in more detail in incorporated US Patent Publication No.20070062852 and US Patent Application Publication No. 20090127005,entitled “System and method for detection with a digitizer sensor” whichis assigned to N-trig Ltd., the contents of which is incorporated hereinby reference.

According to some embodiments of the present invention, each conductiveline of the passive axis is input to an amplifier. In some exemplaryembodiments, the amplifier is a single ended amplifier 445 (FIG. 10).

According to some embodiments of the present invention an independentasynchronous stylus is detected during scanning of a digitizer based ona multi-touch detection method as described in reference to FIG. 10.Typically during digitizer scanning, e.g. for multi-touch detection onlyone axis is sampled while the other is triggered. Although output fromonly one axis may reduce the accuracy of detecting an onset of a stylustransmitting pulse, the present inventors have found that the accuracypermitted is adequate for at least a coarse detection of an appearanceof stylus pulse. Optionally, once fine detection mode is activated, thedigitizer switches to single touch mode and/or samples outputs from boththe triggering and detection axis of the digitizer. Optionally, once astylus signal is determined to be lost, multi-touch detection isreinitiated.

Alternatively, multi-touch detection is supported throughout stylusdetection and tracking, for example, as described in more detail inreference to FIG. 14. In some exemplary embodiments, to support stylusdetection and tracking together with multi-touch, during line samplingperiods, the output from the triggered axis including triggered lines302 is sampled as well as the output from the passive axis includingpassive lines 301. Typically, the gain of the triggered lines isadjusted to avoid saturation when detecting stylus pulsed signals onlines transmitting a triggering signal.

Typically, during scanning of the digitizer sensor, e.g. for multi-touchdetection a plurality of line sampling periods are spread over asubstantially entire period of each refresh cycle, e.g. each linesampling period. This is due to repeated sampling of the lines on oneaxis of the grid for each of a line on the orthogonal axis. A linesampling period is a chunk sampling period over which sensor lines fromone axis of the digitizer are sampled in response to triggering of asensor line on the other axis of the digitizer. Typically, each linesampling periods is devoted to sampling outputs on one axis due to asingle triggering event of the other axis. The number of line samplingperiods, typically equal the number of triggering periods. In someexemplary embodiments, each line sampling period lasts for 0.32 msec or0.64 msec. According to some embodiments of the present invention, astylus transmission signal, e.g. a beacon signal having width 1.28 mseccan be detected on more than one line sampling period of stylusscanning, e.g. typically over two line sampling periods. According tosome embodiments of the present invention, as long as there is nosampling hole greater than a pre-defined fraction, e.g. ½ of a width ofthe stylus transmitting pulse, the pulse will overlap with at least onefull sampling window and the stylus can be detected immediately.

In some exemplary embodiments, a signal to noise ratio of a detectionsignal can be improved by artificially combining detected signals fromtwo consecutive line sampling periods into one continuous signal beforedetermining an amplitude level of the signal. In order to combine thetwo signals, a phase shift due to a break in time between the twoconsecutive line sampling periods needs to be taken into account. Thephase angle between the two detected signals is defined by a period ofthe time break and the frequency of the beacon pulse 110 and one of thedetected signal outputs is shifted by the defined rotation. Oncecombined, output level of the combined signal can be used to determinedetection of a stylus pulse.

Multi-Touch Detection Scanning with Differential Setup

Reference is now made to FIGS. 11A and 11B showing exemplary simplifiedcircuit diagrams for touch detection based on a multi-touch detectionmethod with differential amplifiers for use with some embodiments of thepresent invention. In some exemplary embodiments, the amplifier is adifferential amplifier 340 where one input to differential amplifier 340is ground. According to some embodiments of the present invention, whenone of the inputs to the differential amplifier is ground, eachtriggering event of an active line 302 provides for sampling only halfof the passive lines 301. According to some embodiments of the presentinvention, connection to ground is toggled between each of the inputs(positive and negative) of differential amplifier 340 so that all linesof the sensor lines can be detected. In some exemplary embodiments anactive line 302 is triggered once to detect all positive inputs to thedifferential amplifiers 340 (FIG. 11A) connection to ground is thentoggled and the same active lines is triggered again so that allnegative inputs to the differential amplifiers 340 are detected (FIG.11B).

It is noted that although in FIGS. 10 and 11A and 11B one axis is shownas the active axis and the other axis is shown as the passive axis,either one of the axes can serve as the active or passive axis.Furthermore, it is noted that the active and passive axes can bedynamically switched by ASIC 16 together with digital unit 20.

According to some embodiments of the present invention, during eachsweep only half the conductive lines are sampled and the resolution inthe sampling axis is thereby reduced. In some exemplary embodiments, afirst half of the lines, e.g. every other line, are sampled over onerefresh cycle, and a second half of the lines are sampled in asubsequent refresh cycle. However, it is noted that although theresolution in this case is compromised, refresh rate is increased.

According to some embodiments of the present invention, stylus detectionis provided concurrently with finger touch (or conductive object)detection. Typically, a frequency output of the stylus signal is otherthan the frequency used for finger detection, e.g. with an orthogonalfrequency or a frequency far enough away from a finger detectionfrequency so that finger and stylus detection can be differentiated.According to some embodiments of the present invention, output from boththe passive and active lines is detected, e.g. via amplifiers so thatstylus interaction can be detected concurrently with finger interaction.

Reference is now made to FIG. 11C showing an exemplary time line showingexemplary line sampling periods for multi-touch detection method withdifferential amplifiers for use with some embodiments of the presentinvention. According to some embodiments of the present invention, inresponse to triggering of sensor line on a digitizer a line over aduration 800, sampling period 810 is used to sample a first half of thesensor lines, e.g. sensor lines 301 connected for example to a positiveinput to a set of differential amplifiers. Subsequently while the sameline is triggered over duration 800 a second line sampling period 820samples a second half of the sensor lines connected for example to anegative input to the set of differential amplifiers. Subsequently, anext line is triggered, and sampling of the positive and negative inputsof the differential amplifier is repeated. This process is continueduntil all the lines on one axis are scanned, e.g. all the linesdesignated for multi-touch are scanned. Exemplary line sampling periodsfor scanning 4 lines is shown in FIG. 11C. Multi-touch detection isdescribed with further details, for example in incorporated U.S. Pat.No. 7,372,455 and US Patent Publication No. 20070062852 and US PatentPublication No. 20090127005. Additionally, further details regardingmulti-touch detection is described in US Patent Publication No.20090251434 entitled “Multi-Touch and Single Touch Detection” assignedto N-Trig Ltd., and the contents of which is incorporated herein byreference.

As can be appreciated by the persons skilled in the art, the singletouch detection methods described in reference to FIGS. 4-5 isinherently faster and more economical in terms of processing as comparedto the multi-touch detection methods described in reference to FIGS. 10,11A-11B that requires sequential scanning of the conductive lines, e.g.the passive lines.

Shortened Method for Multi-Touch

According to an aspect of some embodiments of the present inventionthere is provided a multi-touch sensitive computing system and methodthat provides for identifying portions of the multi-touch sensitivesensor that requires scanning to detect multi-touch positions of userinteractions. According to some embodiments of the present invention,portions of a sensor affected by user interaction are first identifiedprior to scanning and once identified only the lines associated with theidentified portion are scanned.

Reference is now made to FIG. 12A showing a schematic illustration ofdigitizer sensor outputs along a second axis of a digitizer sensor inresponse to simultaneously triggering sensor lines along a first axisused to identify interacting lines of the sensor along the second axisin accordance with some embodiments of the present invention. Accordingto some embodiments of the present invention, to identify interactinglines 3010 prior to scanning, a group of sensor lines 302, e.g. allsensor lines 302 are triggered simultaneously with an AC triggeringsignal 360. Optionally, sensor lines 302 are divided into groups, andlines from each group are triggered simultaneously withindistinguishable (or same) signals. In response to the simultaneoustriggering, outputs from cross lines 301 are sampled and amplitudes ofthe output signals are examined to identify interacting lines 3010 amongcross lines 301. Outputs with the strongest signals, e.g. signal over apre-defined amplitude are singled out as interacting lines.

According to some embodiments of the present invention, identifiedinteracting lines 3010 along the second axis are scanned (for example,sequentially triggered) to determine locations of touch interaction.Referring now also to FIG. 12B showing a schematic illustration ofsensor outputs when scanning interacting lines of the second axis of thesensor to determine multi-touch interaction in accordance with someembodiments of the present invention. According to some embodiments ofthe present invention, during a second stage of detection, thetriggering axis is switched and only interacting lines 3010 aresequentially triggered to locate various finger touch 46 positions. Inresponse to each triggering event e.g. triggering events at times t₁,t₂, . . . t₅, output from all cross-lines 302 are sampled to obtaintwo-dimensional information regarding the various finger touch 46locations and/or touch junctions 42 on interacting lines 3010.

According to some embodiments of the present invention, output from eachof sensor lines are input to differential amplifiers and detection ofoutput signals are obtained in a two step process once to detect allpositive inputs to the differential amplifiers 340 (FIG. 11A) connectionto ground is then toggled and the same active lines is triggered againso that all negative inputs to the differential amplifiers 340 aredetected (FIG. 11B).

Reference is now made to FIG. 12C showing an exemplary time line ofexemplary line sampling periods for a shortened method for multi-touchdetection method with differential amplifiers for use with someembodiments of the present invention. According to some embodiments ofthe present invention, a digitizer first checks all the lines to detectinteracting lines, e.g. lines 3010 sampling period 801. Detection is ina two stage process. In a first stage, all lines are triggered along oneaxis and half the lines on the other axis are sampled over a firstsampling period 811 and the second set of lines are detected over asecond sampling period 821. In some exemplary embodiments, once theinteracting line are identified, during a second stage scanning of onlythe identified interaction lines is performed. Optionally, interactionlines are identified on both axes and only interaction lines identifiedon the sampling axis are sampled. Scanning time can be significantlyreduced and thereby the refresh cycle of the digitizer. It is noted thatalthough duration (or width) of sampling periods 811 and 821 are shownto be longer than line sampling periods 820 and 810, optionally all ofsampling periods 811, 821, 810, and 820 have a common duration.

Typically, the refresh period is a function of the number of linesidentified as interacting lines, e.g. the number of line samplingperiods 810 and 820 required per refresh cycle. In some exemplaryembodiments, a pre-defined number of lines are defined to be selectedfrom scanning so that a constant refresh cycle period can be maintainedregardless of changes in the number of interacting lines and the styluscan synchronized to a point in the refresh cycle. Optionally, 5 or 10lines are selected as the pre-defined number of lines. In some exemplaryembodiments, if less than 5 (or 10) lines are identified dummy lines areadded to maintain a constant refresh cycle period.

Further details regarding multi-touch detection described in referenceto FIGS. 12A-12C is described in US Patent Publication No. 20090273579entitled “Multi-Touch Detection” assigned to N-Trig Ltd., and thecontents of which is incorporated herein by reference.

According to some embodiments of the present invention, duringsimultaneous triggering of all lines to identify interacting lines asdescribed in reference to FIGS. 12A and 12B, the differential amplifiersare at minimum gain and the stylus signal while in hover mode can not beeasily detected. In some exemplary embodiments, digitizer 100additionally samples output from the triggering lines to obtained highergain readings so that the stylus pulse can be detected during a hoveringmode.

Alternatively, in some exemplary embodiments, stylus detection during aperiod when all the lines on one axis are simultaneously triggered isavoided and stylus detection is only performed during sequentialscanning of the lines. In such a case multiple transmission periods ofthe stylus pulse will be required before the full transmission periodcan be covered.

Reference is now made to FIGS. 13A and 13B showing a simplifiedexemplary time line for detecting a stylus pulse after repeated refreshcycles of a digitizer scanning 10 selected lines in accordance with someembodiments of the present invention. In some exemplary embodiment, whenonly 10 selected conductive lines are scanned, a time period over whichall the lines on one axis are simultaneously triggered is spread over 6ms and a time period 950 over which the 10 lines are scanned occupies a12 msec period, 1.2 ms per line resulting in a refresh rate every 18msec while a stylus transmits every 15 msec. If stylus detection isavoided when the lines are simultaneously triggered, detection of thefirst 6 msec is potentially lost. However, after a plurality of repeatedcycles, positive detection of the stylus can be obtained, e.g. after 4cycles. According to some embodiments of the present invention, due to amismatch between a refresh rate of the digitizer, e.g. set at 18 msecrefresh period and a transmission period of the stylus set at 15 msecscanning of sensor lines over subsequent refresh periods fill in aninitial period in each refresh cycle where stylus detection is avoided.In the example shown in FIG. 13, a stylus signal can be picked up after1-4 refresh periods of the digitizer. Optionally, stylus detection isavoided for a time period over which all the lines on one axis aresimultaneously triggered plus a buffer period equaling the duration ofthe expected stylus pulse, e.g. 1.28 and the duration covered by chucksampling period 950 is shortened by the duration of the expected styluspulse, e.g. 1.28.

According to some embodiments of the present invention, coarse detectionof the stylus during multi-touch scanning methods, e.g. with single endamplifier (FIG. 10) and/or differential set-up (FIGS. 11A, 11B, 11C,12A, 12B, 12C) is by determining energy levels of output (in frequencyof stylus AC burst signal) over one or more, e.g. typically more thanone, line sampling period. Typically, coarse detection is determined ifthe energy level exceeds a pre-defined threshold for stylus detection.During this period, a first appearance in time of a stylus signal withinone of the line sampling periods coarsely defines the location of thestylus signal in time.

Optionally, in response to a stylus signal being identified and itstiming coarsely detected, a digitizer reverts to detecting the stylus(and finger touch detection) based on a differential setup as describedin reference to FIGS. 4 and 5. Fine detection, synchronization andtracking may be as described in reference to FIG. 6.

Reference is now made to FIG. 14 showing a simplified exemplary timeline for supporting multi-touch detection with detection of anautonomous asynchronous stylus after synchronization in accordance withsome embodiments of the present invention. According to some embodimentsof the present invention, multi-touch detection is supported duringdetection of an autonomous asynchronous stylus by using a time divisionmethod with defined time slots for finger touch detection and stylusdetection. Typically, appearance of a stylus pulse controls the timingof detection since it is an autonomous signal. In some exemplaryembodiments, a beacon pulse, e.g. pulse 110 together with a trailingpulse, e.g. pulse 130 is received during a first period of 2.6 msec of adigitizer refresh cycle (of 7.5 msec). In some exemplary embodiments,stylus detection is followed by a period over which 5-10, e.g. 5 of thesensor lines in digitizer 12 are selected using methods described inreference to FIG. 12A. In a following refresh cycle, stylus tip pressureis reported over a 1.3 msec period. In some exemplary embodiments, a 6.2msec period is left after pressure signal sampling during which the 5selected sensor lines can be scanned using methods described inreference to FIG. 12B. Typically such a time line is used to support upto two simultaneous finger touch interactions. Optionally the multitouch detection is lengthened to several refresh cycles to support morefingers.

It is noted that the present invention is not limited to the technicaldescription of the digitizer system described herein. The presentinvention may also be applicable to other digitized sensor and touchscreens known in the art, depending on their construction. The presentinvention may also be applicable to other touch detection methods knownin the art.

The terms “comprises”, “comprising”, “includes”, “including”, “having”and their conjugates mean “including but not limited to”.

The term “consisting of” means “including and limited to”.

The term “consisting essentially of” means that the composition, methodor structure may include additional ingredients, steps and/or parts, butonly if the additional ingredients, steps and/or parts do not materiallyalter the basic and novel characteristics of the claimed composition,method or structure.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable sub-combination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

What is claimed is:
 1. A method for operating a digitizer with a styluswherein the digitizer includes a grid based digitizer sensor includingconductive lines arrayed along a first and second axis of the digitizersensor, the method comprising: triggering at a defined time within arefresh cycle of the digitizer at least a portion of the conductivelines with a triggering signal; detecting finger touch interaction withthe digitizer during the refresh cycle in response to the triggering;transmitting a signal by the stylus; sensing the signal of the styluswith the digitizer sensor during the refresh cycle of the digitizer;determining a time within the refresh cycle of the digitizer forsampling the signal transmitted by the stylus; and detecting position ofthe stylus in subsequent refresh cycles responsive to sampling thesignal transmitted by the stylus at the determined time within therefresh cycle.
 2. The method according to claim 1, comprisingsimultaneously detecting finger touch interaction and stylus interactionwith the digitizer.
 3. The method according to claim 1, wherein the timewithin the refresh cycle of the digitizer is determined from outputobtained from 1-4 conductive lines from which the signal of the stylusis most strongly detected.
 4. The method according to claim 1, whereindetermining the time within the refresh cycle of the digitizer forsampling the signal is performed while the stylus is hovering over thedigitizer.
 5. The method according to claim 1, comprising samplingoutput from only one of the first or the second axis of the digitizerfor detecting the finger touch interaction.
 6. The method according toclaim 5, comprising switching to sampling output from both the first andthe second axis for sampling the signal transmitted by the stylus. 7.The method of claim 1, wherein the signal transmitted by the stylusincludes encoded information.
 8. The method according to claim 7,wherein the encoded information includes information regarding anoperational state of the stylus.
 9. The method according to claim 7,wherein the encoded information includes information regarding usercommand.
 10. The method according to claim 7, wherein the encodedinformation is selected from the group including: identification of thestylus, right click mode of the stylus, eraser mode of the stylus,pressure on tip of the stylus, and user selected color.
 11. The methodaccording to claim 7, wherein the information is encoded using at leastone of amplitude shift keying, phase shift keying and frequency shiftkeying.
 12. The method according to claim 7, wherein the information isencoded with digital encoding.
 13. The method according to claim 7,wherein the information is encoded with analog encoding.
 14. The methodaccording to claim 7, wherein the digitizer decodes the encodedinformation responsive to sampling the signal transmitted by the stylus.15. The method according to claim 1, wherein the digitizer identifiesthe signal of the stylus based on detection of a frequency of thesignal.
 16. The method according to claim 1, wherein the signaltransmitted by the stylus includes a train of pulses in succession andwherein the digitizer samples the train of pulses over the refreshperiod of the digitizer.
 17. The method according to claim 16, whereinthe train of pulses is AC pulses.